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Abstract:

Roughage level and method of corn
processing were evaluated for the propensity
to cause subacute acidosis in a controlled
acidosis challenge model. Four ruminally
fistulated steers were adapted to a high grain
diet, randomly allocated within a 4 × 4 Latin
square, and fed a corn-based finishing ration
at 2% of BW/day (dry basis) in two equal
feedings. Chopped alfalfa hay was used as
the roughage source and added at 8% of the
diet dry matter or not added. Corn was fed
either whole (WSC) or dry rolled (DRC).
Roughage level and grain processing had no
effect on postchallenge molar percentage of
acetate or total volatile fatty acid production.
An interaction (P<.05) was seen in both percent
propionate and acetate:propionate ratio.
Eliminating roughage in the WSC diet
resulted in increased production of
propionate and a lower acetate:propionate
ratio. Ruminal pH at 3 hours postchallenge
and intake during the recovery period were
lower (P<.05) for 0 vs 8% roughage.
Ruminal pH at 3 and 6 hours postchallenge
was lower (P<.05) for DRC than for WSC.
Intake during the recovery period did not
differ between DRC and WSC. Hours below
pH 5.6 were greater (P<.05) for DRC vs
WSC and for 0 vs 8% roughage. Though
statistically higher (P<.05), no biologically
significant levels of lactate were found for
either DRC or WSC. This study indicates
that adding roughage or feeding WSC vs
DRC reduces the propensity for subacute
acidosis.